support: Raise errors for support requests that are not processed.

Previously, the message string was sent as a success response to
the context, which could have been confusing or ignored when shown
in the support admin view.

analytics/views/support.py

@@ -54,6 +54,7 @@ if settings.BILLING_ENABLED:
         RealmBillingSession,
         RemoteRealmBillingSession,
         RemoteServerBillingSession,
+        SupportRequestError,
         SupportType,
         SupportViewRequest,
         cents_to_dollar_string,
@@ -265,8 +266,11 @@ def support(
             billing_session = RealmBillingSession(
                 user=acting_user, realm=realm, support_session=True
             )
-            success_message = billing_session.process_support_view_request(support_view_request)
-            context["success_message"] = success_message
+            try:
+                success_message = billing_session.process_support_view_request(support_view_request)
+                context["success_message"] = success_message
+            except SupportRequestError as error:
+                context["error_message"] = error.msg
 
     if query:
         key_words = get_invitee_emails_set(query)
@@ -466,14 +470,21 @@ def remote_servers_support(
             )
         if support_view_request is not None:
             if remote_realm_support_request:
-                success_message = RemoteRealmBillingSession(
-                    support_staff=acting_user, remote_realm=remote_realm
-                ).process_support_view_request(support_view_request)
+                try:
+                    success_message = RemoteRealmBillingSession(
+                        support_staff=acting_user, remote_realm=remote_realm
+                    ).process_support_view_request(support_view_request)
+                    context["success_message"] = success_message
+                except SupportRequestError as error:
+                    context["error_message"] = error.msg
             else:
-                success_message = RemoteServerBillingSession(
-                    support_staff=acting_user, remote_server=remote_server
-                ).process_support_view_request(support_view_request)
-            context["success_message"] = success_message
+                try:
+                    success_message = RemoteServerBillingSession(
+                        support_staff=acting_user, remote_server=remote_server
+                    ).process_support_view_request(support_view_request)
+                    context["success_message"] = success_message
+                except SupportRequestError as error:
+                    context["error_message"] = error.msg
 
     email_to_search = None
     hostname_to_search = None

corporate/lib/stripe.py

@@ -434,6 +434,14 @@ class InvalidTierError(Exception):
         super().__init__(self.message)
 
 
+class SupportRequestError(BillingError):
+    def __init__(self, message: str) -> None:
+        super().__init__(
+            "invalid support request",
+            message,
+        )
+
+
 def catch_stripe_errors(func: Callable[ParamT, ReturnT]) -> Callable[ParamT, ReturnT]:
     @wraps(func)
     def wrapped(*args: ParamT.args, **kwargs: ParamT.kwargs) -> ReturnT:
@@ -1164,12 +1172,12 @@ class BillingSession(ABC):
                 f"Cannot upgrade from {plan.name} to {CustomerPlan.name_from_tier(new_plan_tier)}"
             )
 
-    def check_customer_not_on_paid_plan(self, customer: Customer) -> str:  # nocoverage
+    def check_customer_not_on_paid_plan(self, customer: Customer) -> str:
         current_plan = get_current_plan_by_customer(customer)
         if current_plan is not None:
             # Check if the customer is scheduled for an upgrade.
             next_plan = self.get_next_plan(current_plan)
-            if next_plan is not None:
+            if next_plan is not None:  # nocoverage
                 return f"Customer scheduled for upgrade to {next_plan.name}. Please cancel upgrade before approving sponsorship!"
 
             # It is fine to end legacy plan not scheduled for an upgrade.
@@ -3037,8 +3045,8 @@ class RealmBillingSession(BillingSession):
         customer = self.get_customer()
         if customer is not None:
             error_message = self.check_customer_not_on_paid_plan(customer)
-            if error_message != "":  # nocoverage
-                return error_message
+            if error_message != "":
+                raise SupportRequestError(error_message)
 
         from zerver.actions.message_send import internal_send_private_message
 
@@ -3398,7 +3406,7 @@ class RemoteRealmBillingSession(BillingSession):
         if customer is not None:
             error_message = self.check_customer_not_on_paid_plan(customer)
             if error_message != "":
-                return error_message
+                raise SupportRequestError(error_message)
 
             if self.remote_realm.plan_type == RemoteRealm.PLAN_TYPE_SELF_MANAGED_LEGACY:
                 plan = get_current_plan_by_customer(customer)
@@ -3814,7 +3822,7 @@ class RemoteServerBillingSession(BillingSession):
         if customer is not None:
             error_message = self.check_customer_not_on_paid_plan(customer)
             if error_message != "":
-                return error_message
+                raise SupportRequestError(error_message)
 
             if self.remote_server.plan_type == RemoteZulipServer.PLAN_TYPE_SELF_MANAGED_LEGACY:
                 plan = get_current_plan_by_customer(customer)

corporate/tests/test_stripe.py

@@ -56,6 +56,7 @@ from corporate.lib.stripe import (
     RemoteRealmBillingSession,
     RemoteServerBillingSession,
     StripeCardError,
+    SupportRequestError,
     SupportType,
     SupportViewRequest,
     add_months,
@@ -5393,6 +5394,14 @@ class TestSupportBillingHelpers(StripeTestCase):
         self.assertEqual(realm_audit_log.extra_data, expected_extra_data)
         self.assertEqual(realm_audit_log.acting_user, support_admin)
 
+        # Confirm that once a plan has been purchased and is active,
+        # approving a full sponsorship (our version of 100% discount) fails.
+        with self.assertRaisesRegex(
+            SupportRequestError,
+            "Customer on plan Zulip Cloud Standard. Please end current plan before approving sponsorship!",
+        ):
+            billing_session.approve_sponsorship()
+
     def test_approve_realm_sponsorship(self) -> None:
         realm = get_realm("zulip")
         self.assertNotEqual(realm.plan_type, Realm.PLAN_TYPE_STANDARD_FREE)